Expression of protein gene product 9.5 and tyrosine hydroxylase in childhood small round cell tumors

Small round cell tumors of childhood can be histologically ambiguous, can r equire tumor markers for an accurate diagnosis, and include neuroblastoma, peripheral primitive neuroectodermal tumor (pPNET), Ewing's sarcoma (ES), l ymphoma, and rhabdomyosarcoma, Because the cell type of origin for ES remai ns controversial, characterizing gene expression in ES can provide diagnost ic markers and lead to better understanding of tumor biology. We studied RN A expression of the neuronal genes protein gene product 9.5 (PGP 9.5) and t yrosine hydroxylase (TH) by Northern analysis in cell lines and tissue from small round cell tumors. PGP 9.5 showed strong expression in 17 of 17 neur oblastoma cell lines, 9 of 9 pPNET cell lines, and 11 of 11 ES cell lines. PGP 9.5 was weakly expressed in 1 of 1 alveolar rhabdomyosarcoma cell lines but not in 1 of 1 embryonal rhabdomyosarcomas, and weak expression was see n in I of 7 leukemia cell lines. In tumor tissue, all 12 neuroblastomas exp ressed PGP 9.5, as did all 7 pPNET and all 7 ES. PGP 9.5 was very weakly ex pressed in 6 of 9 rhabdomyosarcomas and 1 of 9 lymphomas, TH was expressed only in neuroblastomas, and no TH expression was seen in cell lines or tiss ue from other tumors. As high expression of PGP 9.5 was only found in neura l tumors; PGP 9.5 expression by ES provides further evidence for a neural o rigin of this tumor, whereas TH expression is highly specific for neuroblas tomas, PGP 9.5 expression should allow sensitive detection of minimal resid ual disease for ES and pPNET using reverse transcription-PCR, and the varia bility in TH and PGP 9.5 expression levels in neuroblastomas indicates that expression of both genes should be used for monitoring minimal residual di sease by reverse transcription-PCR.